Well, the guest bathroom is located between my room and the guest room- there is a door from the bathroom into my room and one on the opposite side of the bathroom to the guest room. When I don't have guests, I use that bathroom for morning pee stop and the occasional shower, when I have a guest, it is exclusively theirs and the door is locked from the guest side, ie. inside the bathroom. I could easily stick a screwdriver in the knob to open it from my side, as it is a bathroom knob and they are designed like that, but no guest has ever complained or expressed concern that I could, in fact, open that door, so I don't think the locks issue within your own home is a big deal, unless you've had guests mention it.
You are trusting strangers in your home to treat it respectfully, guests need to have some trust in their hosts that they won't just enter and abuse their privacy.